Hi
I am working on a near field (5-10cm) Non-linear Junction detector using a Arduino uno and a WIFI Shield and wondering what the best shield should be.
For those unfamiliar NLJD is a way of finding electronic devices (even unpowered devices) by inducing a current to flow in around the circuit by placing a RF transmitter close by and then detecting a distortion in the original RF signal due to the non-linear effect of semiconducting junctions. The distortion is typically seen as harmonics (2nd and 3rd) in a receiver. Is anyone interesting in researching this with me?
Careful design, separating the transmitting coil and the electronics, then by careful "nulling out" or calibration of all remaining unintentional distortions.
Seems interesting project to find out if a person hiding recorder/mobile phone/tap wire. I don't think wi-fi shield is suitable, because it intentionally made to work with a packets of data. Better to use RF module in CW mode or OOK, between legally available 315 / 433 / 915 MHz.
315 looks promising, as it's 3-rd harmonics could be easily registered with 3$ SI4432 module.
For 433 band, satellite tuner DVB-S may works as a receiver, so obviously it's cost more than 3$.
915 is most problematic band, as I can't see easy way to build 2.745 GHz receiver , same time sensitivity could be the best in this range.
Actually, these things mostly find un-powered devices as when powered up, the junctions are biased into linear regions, either conducting (bipolar transistors) or non-conducting (FET arrays, parasitic diodes).